In the US, rooftop solar has traditionally been viewed with caution by utilities. Installed by third parties, it cuts utility revenues and at large scale can also create problems for the grid. Because of this, many utilities have fought to keep solar off residential and commercial and industrial (C&I) roofs. In recent years, though, a growing number of utilities have also seen residential and C&I rooftop solar as an opportunity, bringing their own resources to the market.

Compared to ground-mounted installations, however, rooftop solar presents a number of challenges, particularly relating to operations and maintenance (O&M). This white paper aims to provide an overview of the US utility rooftop solar market, and the main challenges it faces in terms of O&M, ahead of Solar PV Operations USA 2018 conference on November 7 and 8, at the Hilton San Diego Mission Valley Hotel in California.

Market overview

In spite of tariffs on imported modules, the US solar market added 2.5 GW of PV in the first quarter of 2018, representing annual growth of 13%, according to the US Solar Market Insight Report from GTM Research and the Solar Energy Industries Association (SEIA). PV accounted for 55% of all new US electricity capacity during the quarter and added more than 2 GW for the 10th straight quarter, the study says.

Of this, 1.4 GW was in utility-scale plants, which have been adding more than 1 GW of capacity every quarter for the last two and a half years. Residential and C&I installations, which make up the bulk of rooftop solar capacity, show a mixed picture. Residential PV installations are essentially flat on a year-on-year and quarter-on-quarter basis, says the SEIA. Meanwhile non-residential PV, essentially C&I, fell 34% quarter-on-quarter but was up 23% year-on-year.

Within the rooftop solar segment there are a range of ownership models. Historically the most common was where the property owner also owned the solar array, which was usually installed and maintained by an independent installer. Around 2011, this was overtaken by lease models where ownership of the solar arrays remained with the installer and the rooftop owner was paid a fixed fee for giving up their roof. But direct ownership began to overtake lease models again last year.

What has also changed in recent years is that utilities have started participating in the residential and C&I markets, either through lease programs or through the development of community solar, which may incorporate a mix of rooftop and ground-mounted PV.

Utility-led rooftop initiatives

Utility-led rooftop initiatives have tended to be led by unregulated utilities such as Duke Energy, Edison International, NextEra and NRG. Since 2014, though, regulated utilities such as Arizona Public Service and Tucson Electric Power have also looked to enter the rooftop space, although their ability to rate-base the cost of solar investments has irked installers.

Utilities are motivated to enter the market because it enables them to maintain customer relationships and revenues, even if the latter may be reduced somewhat through solar self-consumption. Some studies have indicated that community solar initiatives might also help restore customer trust in utilities.

Furthermore, forward-thinking utilities see rooftop solar as a way of gaining experience with next-generation grid architectures that rely heavily on distributed energy resources. In New York, for example, Consolidated Edison was able to save around $1bn on a substation upgrade by building a solar-plus-storage microgrid in the Brooklyn-Queens neighborhood.

But according to Matt Herman, co-owner and operations and maintenance sales manager at residential and C&I PV specialist Namasté Solar, utilities looking to invest in rooftop solar should be aware that there are significant O&M issues to be considered. In particular, the small size and distributed nature of rooftop solar installations means O&M costs can be significantly higher than for utility-scale plants, particularly if individual locations are spread far and wide.

Utilities must “try to maximize the value of any site visits,” he says. “Another recommendation is ‘be close to the sites.’ We’ve been pretty careful to take on projects that are really in our backyard, that we can service without a ton of windshield time.”

O&M considerations

Having to roll trucks for faults on very small arrays is a major source of cost in rooftop solar O&M. This problem is compounded by the fact that many rooftop systems are old and/or inexpensive, so often lack remote monitoring and control capabilities. On top of this, rooftop solar O&M technicians must comply with stringent working-at-height regulations. “I would say it is the biggest challenge when maintaining rooftop solar systems,” says Neil Bautista, director of services at BayWa r.e. Solar Systems LLC.

Tie-off points, skylight guards and permanent delineation are not typically addressed during system design, he says, and “there is additional cost to incorporate these safety provisions during construction if the facility does not already have them in place.”

Ian Fifield, an ex-utility employee who is now C&I manager at SOLV, Inc, says: “Safety plays a significant role in how you maintain these rooftop projects. It can also significantly increase the cost of doing O&M work, which by far has been one of our biggest hurdles.”

Outlook and conclusions

When taking over O&M for rooftop assets, SOLV has typically found that up to 80% of systems have safety issues that the owner has to be notified of, Fifield says. Around 90% of these issues are related to skylights and unprotected edges. These challenges mean rooftop O&M costs can be almost double what utilities might expect for ground-mounted system. It is unclear how these costs might change in future, when solar is increasingly expected to be tied to battery storage.

Batteries could add slightly to the O&M burden, although they will likely be housed in basements and garages rather than on roofs, making them easier to service. At the same time, battery systems tend to come with sophisticated power management systems, which could improve the potential for remote monitoring and servicing of rooftop solar arrays. And any innovation which reduces the need to get on a roof will help cut cost.

The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag

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